\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
\mbox{flag}_{\mbox{Poland}} = \begin{matrix}{ \mbox{ white } \\ \mbox{ red } \\}\end{matrix}
\end{equation*}
\end{document}
